Lab Notes Gems & Gemology, Summer 2019, Vol. 55, No. 2

Exsolved Particles with Natural Appearance Within Flux-Grown Pink Synthetic Sapphire

Platinum platelet (left) and channels of exsolved flux within a flux-grown synthetic sapphire.
Figure 1. Left: Reflective platinum platelet with negative hexagonal growth within a flux-grown pink synthetic sapphire; field of view 2.34 mm. Right: Channels of exsolved interconnected flux; field of view 4.79 mm. Photomicrographs by Britni LeCroy.

The Carlsbad laboratory recently examined unusual exsolved flux particles in a flux-grown pink synthetic sapphire. The specimen, mounted in a ring, had an estimated weight of 13.07 ct and a refractive index of 1.760–1.770. It displayed a typical pink sapphire spectrum with a handheld spectroscope. Strong red fluorescence was seen under both long-wave and short-wave UV. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) detected high levels of platinum; the concentrations of iron, beryllium, titanium, vanadium, and gallium were either below the detection or quantification limit.

Microscopic examination revealed further evidence of a synthetic origin: a single reflective platinum platelet with negative hexagonal growth through the center (figure 1, left). Also observed were interconnected channels of exsolved flux creating fingerprints (figure 1, right).

Linear stringers of flux particles within natural corundum.
Figure 2. Fine rounded flux particles aligned into linear stringers resembling fingerprints and silk clouds seen within natural corundum. Photomicrograph by Britni LeCroy; field of view 1.73 mm.
A potentially challenging inclusion was seen in the form of minute rounded flux particles aligned in organized linear rows (figure 2), which displayed a striking resemblance to fingerprints and silk clouds commonly seen within natural corundum. These particles were observed in relative abundance at varying depths. Grid-like exsolved solid inclusions have been mentioned in the literature as possible properties of synthetic corundum (R.W. Hughes et al., Ruby & Sapphire: A Gemologist’s Guide, Lotus RWH Publishing, Bangkok, 2017). It has not been stated how abundant these natural-looking fingerprints are within flux-grown synthetic material, but this type of inclusion is rarely seen at the Carlsbad laboratory. Identifying the natural or synthetic origin of a stone with this type of natural-looking inclusion can be challenging. If a gem material is suspected of being synthetic, it is advisable to submit it to a gemological laboratory.

Britni LeCroy is a staff gemologist at GIA in Carlsbad, California.